Methods for imperfect insulating film electrical thickness/capacitance measurement

ABSTRACT

Methods for determining an electrical parameter of an insulating film are provided. One method includes measuring a surface potential of a leaky insulating film without inducing leakage across the insulating film and determining the electrical parameter from the surface potential. Another method includes applying an electrical field across the insulating film. Leakage across the insulating film caused by the electrical field is negligible. The method also includes measuring a surface potential of the specimen and determining a potential of the substrate. In addition, the method includes determining a pure voltage across the insulating film from the surface potential and the substrate potential. The method further includes determining the electrical parameter from the pure voltage. The electrical parameter may be capacitance or electrical thickness of the insulating film.

PRIORITY CLAIM

This application is a divisional application from prior U.S. applicationSer. No. 10/754,332 filed Jan. 9, 2004, which claims priority to U.S.Provisional Application No. 60/440,516 filed Jan. 16, 2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention generally relates to methods for determining one or moreelectrical parameters of an insulating film. Certain embodiments relateto methods for imperfect insulating film electrical thickness and/orcapacitance measurements.

2. Description of the Related Art

Fabricating semiconductor devices such as logic and memory devicestypically includes processing a substrate such as a semiconductor waferusing a number of semiconductor fabrication processes to form variousfeatures and multiple levels of the semiconductor devices. For example,insulating (or dielectric) films may be formed on multiple levels of asubstrate using deposition processes such as chemical vapor deposition(“CVD”), physical vapor deposition (“PVD”), and atomic layer deposition(“ALD”). In addition, insulating films may be formed on multiple levelsof a substrate using a thermal growth process. For example, a layer ofsilicon dioxide may be thermally grown on a substrate by heating thesubstrate to a temperature of greater than about 700° C. in an oxidizingambient such as O₂ or H₂O, Such insulating films may electricallyisolate conductive structures of a semiconductor device formed on thesubstrate.

Measuring and controlling electrical parameters of insulating films suchas capacitance is an important aspect of semiconductor devicemanufacturing. A number of techniques are presently available formeasuring capacitance of insulating films.

One example of a technique that can be used to measure the capacitanceof insulating films is the mercury probe CV technique. This techniqueincludes using the mercury probe as an electrode and making physicalcontact between the probe and the top of the insulating film. A voltageis then applied to the insulating film, and the capacitance of the filmis measured. Such measurements have the disadvantages of requiringcalibration of the surface contact area, variation of the film thicknessin the measurement area due to pressure applied on the surface of thefilm during measurement, and frequent variations in the mercury probedue to mercury oxidation.

Another technique that can be used to measure the capacitance ofinsulating films is the MOS Cap CV technique. This technique utilizes ametal or a heavily doped polysilicon (poly-Si) electrode to measurecapacitance of insulating films by supplying an electric voltage on theelectrode. Such measurements have a long history and establishedutility, however, the weakness of the measurement is the length of timeneeded to obtain results. For example, it normally takes a few days tomake such conductive electrode measurements. Therefore, such a techniqueis not suitable for in-line capacitance monitoring in many manufacturingsituations.

Non-contacting electrical test methodologies have been developed toprovide electrical capacitance, electrical thickness, and electricalconductivity measurements. Non-contact electrical measurement techniqueshave unique advantages in that no modifications to the surface of theinsulating film occur during measurement, no contamination is introducedto the fab due to the measurement, the measurements have excellentstability and repeatability, and the measurements can produce resultsrelatively quickly. These techniques, typically, use a charge generationsource such as a corona generator and a non-contacting voltagemeasurement sensor such as a Kelvin probe or a Monroe probe to determinethe electrical properties of the films. Examples of such techniques areillustrated in U.S. Pat. Nos. 5,485,091 to Verkuil, 6,097,196 to Verkuilet al., and 6,202,029 to Verkuil et al., which are incorporated byreference as if fully set forth herein.

A non-contacting pure capacitance and electrical thickness test methodfor imperfect insulators is described in U.S. Patent Application Ser.No. 60/394,835 entitled “Methods and Systems for Determining a Propertyof an Insulating Film,” filed Jul. 10, 2002, which is incorporated byreference as if fully set forth herein. This method includes measuringboth capacitance and conduction or leak rate under a given bias todetermine the real capacitance and/or electrical thickness of imperfectinsulators.

SUMMARY OF THE INVENTION

An embodiment of the invention relates to a method that includesmeasuring a surface potential of a leaky insulating film withoutinducing leakage across the insulating film. The method also includesdetermining an electrical parameter of the insulating film from thesurface potential. The electrical parameter may be capacitance orelectrical thickness of the insulating film.

An additional embodiment relates to another method for determining anelectrical parameter of an insulating film. A specimen may include theinsulating film formed on a substrate. The substrate may include p typesilicon, n type silicon, epitaxial silicon, a semiconductor material, aconductive material, a silicon on insulator (SOI) substrate, or a filmstack. The film stack may include one or more layers that areinsulating, conductive, or insulating and conductive.

The method includes applying an electrical field across the insulatingfilm. Leakage across the insulating film caused by the electrical fieldis negligible. In this manner, the electrical field does not alter theelectrical parameter of the insulating film. In some embodiments, theelectrical field is about 0.0001 MV/cm to about 1 MV/cm. In otherembodiments, the electrical field is less than about 0.2 MV/cm. In yetanother embodiment, the electrical field is about 0 MV/cm.

The method also includes measuring a surface potential of the specimen.In one embodiment, applying the electrical field across the insulatingfilm and measuring the surface potential are performed withoutcontacting a surface of the specimen. In another embodiment, applyingthe electrical field across the insulating film and measuring thesurface potential include contacting the surface of the specimen. Inaddition, measuring the surface potential may be performed in thepresence of a background light.

In addition, the method includes determining a potential of thesubstrate. In one embodiment, the potential of the substrate isdetermined experimentally. In another embodiment, the potential of thesubstrate is determined theoretically.

The method further includes determining a pure voltage across theinsulating film from the surface potential and the substrate potential.Furthermore, the method includes determining the electrical parameter ofthe insulating film from the pure voltage. The electrical parameter maybe capacitance or electrical thickness of the insulating film. In someembodiments, the method may include determining an optical or physicalthickness of the insulating film and determining a dielectric constantof the insulating film from the capacitance and the optical or physicalthickness. In other embodiments, the method may include obtaining anoptical thickness from a host computer and determining a dielectricconstant of the insulating film from the capacitance and the opticalthickness. Such embodiments may also include reporting the dielectricconstant to the host computer.

In one embodiment, the method may include altering a parameter of aprocess tool in response to the electrical parameter using a feedbackcontrol technique or a feedforward control technique. In anotherembodiment, the method may be performed during a semiconductorfabrication process. In one such embodiment, the method may includealtering a parameter of a process tool in response to the electricalparameter using an in situ control technique.

A further embodiment relates to another method for determining anelectrical parameter of an insulating film. A specimen may include theinsulating film formed on a substrate. This method may include applyingan electrical field across the insulating film. Leakage across theinsulating film caused by the electrical field is negligible. Theinsulating film has a thickness such that a potential of the substrateis negligible. In one embodiment, the thickness of the insulating filmis greater than about 400 Å. In another embodiment, the thickness of theinsulating film is greater than about 1800 Å. The method also includesmeasuring a surface voltage of the specimen. Measuring the surfacevoltage of the specimen may be performed in accumulation, depletion,inversion, or a combination thereof. In addition, the method includesdetermining the electrical parameter of the insulating film from thesurface voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will become apparent uponreading the following detailed description and upon reference to theaccompanying drawings in which:

FIG. 1 is a partial cross-sectional view of an embodiment of aninsulating film formed on a substrate;

FIG. 2 is a schematic diagram of the insulating film formed on thesubstrate;

FIG. 3 is an exemplary graph of surface voltage versus deposited coronacharge for an insulating film of thermal oxide having a thickness of1900 Å;

FIG. 4 is an exemplary graph of the short term repeatability ofmeasurements on a low k insulating film;

FIG. 5 is an exemplary graph of the dielectric constant correlationbetween measurements made using the techniques described herein andmeasurements made using the mercury probe CV technique;

FIG. 6 is a schematic diagram of a side view of an embodiment of asystem configured to measure electrical parameters of an insulating filmusing non-contacting techniques;

FIG. 7 is a schematic diagram of a side view of an embodiment of acharge deposition on a surface of an insulating film using a coronasource; and

FIGS. 8 and 9 are schematic diagrams of partial cross-sectional views ofalternative embodiments of a corona source.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and will herein be described in detail. Itshould be understood, however, that the drawings and detaileddescription thereto are not intended to limit the invention to theparticular form disclosed, but on the contrary, the intention is tocover all modifications, equivalents and alternatives falling within thespirit and scope of the present invention as defined by the appendedclaims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In all description provided herein, the term “surface voltage” is usedinterchangeably with the term “surface potential.”

The following description generally relates to methods and systems formeasuring pure capacitance and/or electrical thickness of insulatingfilms that are not perfect insulators. The insulating films may have anythickness. In a common implementation, the films in question may beproduced in processes of semiconductor device manufacturing. In someembodiments, the insulating film to be measured is on the top surface ofa substrate such as a silicon wafer. In particular, the followingdescription relates to systems and methods for measuring such insulatingfilms in a non-contact manner, and in the presence of significantimperfect insulation. By using the methods and systems described herein,the effects of leakage through such insulating films can be eliminatedand used to determine various properties of insulating films moreaccurately. Compared to the approaches described above in the“Description of the Related Art,” these techniques are advantageous bycombining high sensitivity, high throughput, high measurement stability,and high repeatability.

Present technology for manufacturing integrated circuits andsemiconductor devices makes extensive use of the formation of insulatingfilms. These films may also be commonly referred to as “dielectriclayers.” In a typical implementation, such an insulating film mayinclude silicon dioxide (“SiO₂”), silicon nitride (“Si₃N₄”), a nitridedform of amorphous SiO₂, which may be commonly referred to as oxynitride(“SiO_(x)N_(y)”), silicon carbon, fluorine-doped oxide, spin-on glasses,organic polymers, and other insulating films. Many other materials arealso commonly used. Such films, typically, have high insulating quality.However, some films may be very leaky due to high film defect density orsimply because the film is too thin. For example, relatively thin films(i.e., films having a thickness of less than about 8 nm) may departsubstantially from ideal insulating behavior. That is, such films mayallow significant amounts of current to flow through the insulatingfilm.

For insulating films such as SiO₂, significant departure from a perfectinsulator can occur even for thick films. For example, significantdepartures from a perfect insulator may occur at thicknesses of greaterthan about 30 nm, or even greater than about 50 nm. Such leaky films mayinclude materials commonly known as “low-k” or “high-k” insulatingfilms, where “k” refers to the real part of the dielectric constant asmeasured at electrical frequencies. A low-k insulating film may includeany material having a dielectric constant lower than about 3.9. Suchlow-k insulating films are generally used when reduced film capacitanceper unit area is desired. Examples of commercially available low-kdielectric materials include, but are not limited to, proprietarymaterials known as Silc™, Black Diamond™, CORAL™, and Flare™. A high-kinsulating film may include any material having a dielectric constant ofgreater than about 3.9. A high-k insulating film is often used whenincreased film capacitance per unit area is required for deviceoperation. Examples of high-k materials include, but are not limited to,tantalum pentoxide (“Ta₂O₅”), hafnium dioxide (“HfO₂”), aluminumtrioxide (“Al₂O₃”), and zirconium dioxide (“ZrO₂”). It is to beunderstood that the methodology described herein is not specific to anycomposition or thickness of insulating film.

Such insulating films may be formed, for example, by deposition orthermal growth on a conductive or semiconductor substrate. The substratemay include, but is not limited to, silicon, epitaxial silicon,silicon-on-insulator (“SOI”), or another semiconductor or conductivematerial such as gallium arsenide or indium phosphide. The substrate maybe a P-type silicon substrate or an N-type silicon substrate. Thesubstrate may also include any substrate commonly found and/or processedin semiconductor fabrication facilities, which may be commonly referredto as a “wafer.” In some cases, the substrate may include a film stackthat includes one or more layers that are insulating, conductive, orinsulating and conductive. For example, the insulating film of interestmay be the top layer of a stack of insulators, insulators andconductors, or conductors. In other embodiments, the insulating filmsmay be a single layer or multiple layers deposited or grown on aconductive or semiconductor substrate. The insulating film may have athickness ranging from about 1×10⁻⁴ μm to about 100 μm. The thickness ofthe insulating film may vary, however, depending on parameters of theinsulating film and the selected capacitance per unit area. As usedherein, a “specimen” includes an insulating film formed on a substrate.

For simplicity of illustration, FIG. 1 illustrates a single layer ofinsulating film 10 formed on substrate 12. The insulating film may beschematically illustrated as shown in FIG. 2, in which a resistance ofthe film, R_(film), is electrically in parallel with a capacitance ofthe film, C_(film). R_(film) corresponds to the resistance of this filmto current transport vertically through the film within a given testarea, A. R_(film) may vary with voltage as R_(film)=function (V_(film)).C_(film) corresponds to the capacitance of the region of the insulatingfilm under test. R_(film) may be related to the film resistivity,ρ_(film), by the following equation:R _(film)=ρ_(film) *T _(film) /A,  (1)where T_(film) is the physical thickness of the film, and A is thecross-sectional area of the region of the insulating film being tested.As shown in FIG. 2, V_(A) corresponds to the voltage potential at thetop of the film, and V_(B) corresponds to the voltage of the substrateunderneath the film. V_(B) will be considered to be at ground potentialfor the purpose of the immediate discussion.

In the absence of leakage, the voltage between points A and B, V_(AB),may be defined by the equation for a parallel plate capacitor:Q=V _(AB) *C _(film),  (2)where Q represents charge on the surface of the insulating film. Bymaking depositions of charge, the total of which is recorded as Q_(i)using a non-contacting technique and measuring subsequent voltagemeasurements of the potential, V_(AB), recorded as V_(i) using anon-contacting technique, the capacitance of the film, C_(film), may bedetermined.

Traditionally, capacitance or electrical thickness measurements of aninsulating film on a semiconductor substrate are performed in theaccumulation or inversion regions. By making measurements inaccumulation or inversion, the functional dependency of the substratepotential becomes less important in the theoretical analysis. In atypical non-contact measurement system, the capacitance and electricalthickness are determined from the slope of deposited charge versusvoltage across the insulating film as described below in theaccumulation or inversion region.

For example, in many implementations, the initial charge of the surfaceis unknown, and equation 2 may be rewritten as:Q _(i) =V _(i) *C _(film) +X ₁,  (3)where X₁ is an offset related to the initial charge on the surface of aninsulating film and within the insulating film, but which is unimportantto this discussion. C_(film) may be determined using a least-squares fitof any portion of Q_(i)−V_(i) data with a slope being equal to C_(film)according to equation 3. In a technologically feasible implementation,the voltages, V_(i), corresponding to charge states, Q_(i), may bemeasured at different times denoted as t=t_(i).

Very often, however, insulating films having large film leakage havehigh interface trap densities. As a result, a high bias is required toreach the accumulation or inversion region. Leakage is also a functionof applied electrical field. For example, increasing the applied biasincreases the leakage rate. Therefore, current transporting throughleaky films during measurement can be significant. As a result,increasing the applied bias increases the inaccuracy of the measurementresults. Therefore, standard capacitance and electrical thicknessmeasurements are not suitable for imperfect insulating films. Forexample, without taking current transportation into account during themeasurements, most electrical techniques for measuring insulating filmcapacitance or electrical thickness in the presence of such leakageresult in smaller electrical thickness measurements and largercapacitance measurements.

Since leakage is a function of the electrical field, by carefullyreducing the applied electrical field, the impact due to leakage can bereduced to negligible levels. In this manner, a surface potential of aleaky insulating film may be measured without inducing leakage acrossthe insulating film. In addition, an electrical parameter of theinsulating film may be determined from the surface potential. As aresult, electrical thickness or capacitance can be measured accurately.

Measuring an electrical parameter of a leaky insulating film may includeapplying a relatively small electrical field on an insulating film suchthat leakage across the insulating film induced by the electrical fieldcan be reduced to negligible levels. However, in some cases, thefunctional dependency of the substrate potential may become significant.In the methods described herein, a new technique and method are used tosolve the substrate potential impact on the leaky films with a smallapplied electrical field.

One embodiment of a method for non-contact capacitance and/or electricalthickness measurements for an imperfect insulating film includes thefollowing steps. A specimen, which includes an insulating film formed ona substrate, is biased using a very small amount of charge deposited bya corona charge deposition system, an e-beam charge deposition system,an ion beam charge deposition system, or a plasma-based chargedeposition system. The corona charge deposition system may include oneor more sources such as wire sources, “blanket” sources, or one of thesources described below. In this manner, applying an electrical fieldacross the insulating film may be performed without contacting a surfaceof the specimen.

The amount of charge deposited on the insulating film is small enoughsuch that the leakage current in the insulating film caused by theapplied electrical field is reduced to negligible levels. In thismanner, the amount of charge deposited on the insulating film is alsosmall enough such that the applied electrical field does not alter theelectrical parameters of the insulating film. In one embodiment, theelectrical field applied to the insulating film ranges from about 0.0001MV/cm to about 1 MV/cm. In some embodiments, the electrical fieldapplied to the insulating film may be less than about 0.2 MV/cm. In onesuch embodiment, the electrical field applied to the insulating film maybe about 0 MV/cm. The applied electrical field can be used at afrequency from about 0 MHz to about 1 MHz.

In one embodiment, the surface potential of the specimen may be measuredusing a work function sensor. The work function sensor may be a Kelvinprobe, a Monroe probe, an electrostatic force probe, or an atomic forcemicroscopy (AFM) type probe. As such, the surface potential may bemeasured without contacting a surface of the specimen. The data acquiredusing a charge deposition system and a work function sensor is Q-V data.The surface voltage data can be obtained in a point format or a mapformat by using substantially uniform blankets of charge and mappingV_(surf1) and V_(surf2). Voltage data may be acquired in accumulation(i.e., negative voltages on a p-type wafer or positive voltages on ann-type wafer), depletion, inversion (i.e., positive voltages on a p-typewafer or negative voltages on an n-type wafer), or a combination of twoor three of them.

In other embodiments, the electrical field may be applied to theinsulating film and the surface potential may be measured using acontact technique such as a mercury probe CV technique or a MOS Cap CVtechnique. These techniques involve applying a voltage to the insulatingfilm with a probe or an electrode to generate a relatively smallelectrical field across the insulating film and measuring thecapacitance of the insulating film while the probe or the electrode isin contact with a surface of the specimen. Therefore, a C-V plotter canbe used to acquire C-V data.

The method also includes determining a potential of the substrate. Inone embodiment, the substrate potential is measured experimentally usinga surface photo voltage measurement technique or any other measurementtechnique known in the art. The surface photo voltage measurementtechnique involves measuring the surface voltage in the presence of abackground light. For example, measuring the substrate potential mayinclude illuminating the surface of the specimen with a light sourcesuch as a laser, a multi-wavelength lamp source, or any otherappropriate light source known in the art, and measuring the surfacevoltage. In an alternative embodiment, the substrate potential may bedetermined theoretically using a theoretical model or an empirical modelknown in the art.

In this manner, the “pure” voltage across the insulating film can bedetermined as the difference between the surface potential and thesubstrate potential. Consequently, one or more electrical parameters ofthe insulating film can be calculated from the pure voltage. Some of theelectrical parameters that can be obtained using this technique includecapacitance (C_(Die)), equivalent oxide thickness (EOT), electrical filmthickness (T_(film)), and dielectric constant (κ). The pure voltageacross the insulating film may also be determined at one or more siteson the specimen by performing the above measurements at a specific siteon the specimen or at different sites on the specimen. Therefore, one ormore electrical parameters of the insulating film can be determined forone or more sites on the specimen. Furthermore, a two-dimensional map ofthe electrical parameters across specimen may be generated or displayed.

The real capacitance (C_(Die)) can be determined from the pure voltageacross the insulating film and the deposited charges. For example, whena small electrical field is applied on a leaky insulating film, C_(Die)can be given by the following equation in accumulation, depletion, andinversion:

$\begin{matrix}{C_{Die} = {\frac{( {{\Delta\; V_{Die}} - {\Delta\; V_{Si}}} )}{\Delta\; Q}.}} & (4)\end{matrix}$ΔV_(Die) can be measured using a work function sensor, and ΔV_(Si) canbe measured either by a surface photo voltage method or by modelingusing a theoretical model or an empirical model.

The equivalent oxide thickness can be determined using the dielectricconstant of silicon oxide and the measured capacitance. In a similarmanner, the electrical film thickness can be determined using thedielectric constant of the insulating film and the measured capacitance.For example, if the dielectric constant of the film is known or isassumed, an “electrical film thickness,” T_(film), may be determinedfrom the capacitance. The capacitance of the film may be related to theelectrical thickness using the equation:T _(film)=∈₀ *κ*A/C _(film),  (5)wherein ∈₀ is the free space permittivity of vacuum, and κ is the filmrelative dielectric constant. In this manner, the expression relatingfilm capacitance, electrical thickness, and dielectric constant is thatof a parallel plate capacitor.

If the dielectric constant of the insulating film is not known, thedielectric constant can be determined using the physical thickness ofthe insulating film and either the measured capacitance or thecalculated EOT using one of the following equations:

$\begin{matrix}{{\kappa = \frac{C_{Die}*T_{Physical}}{ɛ_{0}}},{or}} & (6) \\{\kappa = {\frac{3.9*{EOT}}{T_{Physical}}.}} & (7)\end{matrix}$The physical thickness of the film may be estimated from processconditions that were used to form the insulating film or may be measuredindependently using an experimental method. Methods for determining thephysical thickness of the film independently may include, but are notlimited to, x-ray photoelectron spectroscopy (XPS), transmissionelectron microscopy (TEM), step profilometry, and any other techniquesor systems known in the art. Alternatively, the dielectric constant maybe determined from the capacitance and an optical thickness of theinsulating film. Methods for determining the optical thickness of thefilm independently may include, but are not limited to, ellipsometry,reflectometry, and any other techniques known in the art.

In addition, the optical thickness can be obtained from a host computer.The host computer may or may not be coupled to a measurement system usedto perform the measurements described above. For example, the hostcomputer may be coupled to such a measurement system by a transmissionmedium that may include “wired” and “wireless” portions. The opticalthickness obtained from the host computer may have been sent to the hostcomputer from a different measurement system such as an ellipsometer orreflectometer also coupled to the host computer.

The dielectric constant of the insulating film may be determined fromthe capacitance and the optical thickness obtained from the hostcomputer. The dielectric constant may be reported back to the hostcomputer. In some embodiments, the host computer may be located in asemiconductor fabrication facility (a “fab”). The host computer may haveaccess to a fab database through a network or a storage medium coupledto the host computer. The fab database may include a variety ofinformation related to tools and processes carried out in the fab suchas tool history, wafer history, and reticle history. A fab database mayalso include any set of data suitable for use in an overall fabmanagement system. An example of such a system is illustrated in PCTPublication No. WO 99/59200 to Lamey et al., which is incorporated byreference as if fully set forth herein. The host computer may update thefab database with the determined dielectric constant. The informationstored in the fab database may be used for statistical process control(SPC) or other functions.

In this manner, a dielectric constant of an insulating film may bedetermined from a physical or optical thickness and a capacitance thatare independently determined. An independent determination of κ may be atechnologically important aspect for characterizing many dielectricmaterials.

However, it is noted that when the insulating film is relatively thick,the substrate potential impact on the measurement results can benegligible even in the depletion region. For example, the impact of thesubstrate potential on the measurements can be negligible for insulatingfilms having a thickness greater than about 400 Å. This thickness mayvary, however, depending on the composition of the insulating film,other characteristics of the insulating film, and other materialspresent on the substrate. For example, in some cases, the impact of thesubstrate potential on the measurements can be negligible for insulatingfilms having a thickness greater than about 1800 Å. FIG. 3 illustrates agraph of surface voltage versus deposited corona charge (i.e., a Q-Vsweep) for an insulating film of thermal oxide having a thickness of1900 Å formed on a silicon substrate. The slope of deposited chargeversus surface voltage is constant in accumulation, depletion, andinversion. In this case, regardless of the initial state, an extremelysmall amount of charge can be applied to the insulating film, and thechange in surface voltage can be measured and used to determine thecapacitance and electrical thickness of the insulating film.

Therefore, by making measurements in this non-traditional voltage orelectrical field regime, the effects of leakage may be reduced, and evencompletely eliminated, and superior performance can be achieved. Inaddition, the methods described herein have short term repeatability.For example, FIG. 4 illustrates the short-term stability of the EOT fordifferent low-k insulating film having different thicknesses determinedusing the methods described herein. Furthermore, the methods describedherein produce results that can be correlated to measurements performedwith other techniques. For example, FIG. 5 illustrates a correlationbetween dielectric constants determined using the techniques describedherein (as shown on the y-axis) and dielectric constants determinedusing the mercury probe CV technique. Additionally, the capacitance andelectrical thickness of insulating films can be determined accuratelyand rapidly using the methods described herein. Another advantage of thetechniques and methods described herein is the simplicity of the methodsand the ease-of-use. For example, it is possible to develop a singlemethodology to cover all types of insulating films.

In another embodiment, the method may include altering a parameter of aprocess tool in response to one or more electrical parameters of theinsulating film using a feedback control technique. In a furtherembodiment, the method may include altering a parameter of a processtool in response to one or more electrical parameters of the insulatingfilm using a feedforward control technique. In yet another embodiment,the method may be performed during a semiconductor fabrication processor another process. Therefore, the method may include altering aparameter of a process tool in response to one or more electricalparameters of the insulating film using an in situ control technique, ora “real-time control loop.” The process tool may include any processtool known in the art of semiconductor manufacturing such as adeposition tool. In one embodiment, the method may include altering aparameter of a process tool in response to a dielectric constant of aninsulating film, which can be determined as described herein. Theparameter of the process tool may be altered using a feedback controltechnique, a feedforward control technique, and/or an in situ controltechnique.

An example of a system that may be used to perform the techniques andmethods described herein is illustrated in FIG. 6. The system may beconfigured to measure current-voltage characteristics of insulating film14 formed on substrate 16. The system may include wafer chuck 18configured to hold substrate 16 during a measurement process. Waferchuck 18 may also provide a grounding contact to substrate 16. Thegrounding contact may be obtained, for example, from a high pressurecontact using a sharp tungsten carbide needle. The system may alsoinclude high voltage supply 20 coupled to corona gun 22. High voltagesupply 20 may be configured to supply high voltage (i.e., about 6 kV toabout 12 kV) to the corona gun to produce positive or negative coronacharges depending on the polarity of supply 20. Corona gun 22 mayinclude one or more needles 24 coupled to high voltage supply 20.

In addition, the system may include Kelvin probe 26. Kelvin probe 26 mayinclude an electrode coupled to vibrator 28. Movement of probe 26 abovea charged surface may result in an AC voltage representative of thepotential of the charged surface. Kelvin controller 30 may be configuredto convert an AC voltage to a signal corresponding to the voltage of thesurface.

Current flowing through insulating film 14 and substrate 16 from coronagun 22 may be converted to a voltage by current-to-voltage converter 32.This voltage (current) may be integrated by charge integrator 34 toprovide a measure of the charge deposited by corona gun 22 on insulatingfilm 14. The circuits, thus, are configured as a coulombmeter. Thesystem may also include position actuator 36. Position actuator 36 maybe configured to move corona gun 22 and Kelvin probe 26 over substrate16, as shown in phantom in FIG. 6. The system may also include surfacephoto voltage (SPV) device 38. SPV device 38 may be configured to makean SPV measurement using a relatively high intensity light source suchas a xenon flash tube.

The system may further include controller 40 configured to controloperation of the system. Controller 40 may be configured to controlposition actuator 36 and high voltage supply 20 in response to Kelvincontroller 30, current-to-voltage converter 32, and charge integrator34. The controller may also be configured to provide a measurement ofthe current-voltage behavior of insulating film 14 and substrate 16. Thecontroller may be, for example, a dedicated microprocessor-basedcontroller or a general purpose computer.

FIG. 7 illustrates an embodiment of a charge deposition on a surface ofan insulating film using a corona source. As shown in FIG. 7, positivecharge accumulation 42 in p-type silicon substrate 44 may result fromthe deposition of negative charges 46 from negative corona source 48onto surface of oxide layer 50 overlying substrate 44. The coronadischarge may be applied to the area of interest via mask 52. In oneembodiment, it may be necessary for purposes of obtaining accuratethickness measurements, that a uniform density of charge 46 be depositedthrough the aperture in mask 52.

FIGS. 8 and 9 illustrate partial cross-sectional views of alternativeembodiments of a corona source, which may be used to deposit a chargesubstantially uniformly over an area of specimen 54. Specimen 54 mayinclude an insulating film and a substrate as described herein. Thecorona sources may be configured to provide a well-defined andsubstantial beam charge density (to minimize measurement time) havingrelative uniformity (for measurement accuracy) across the selected siteof interest on specimen 54. As shown in FIG. 8, the corona source mayinclude needle 56 and beam shaping electrodes 58 and 60. Beam shapingelectrodes 58 and 60 may be arranged concentric with an axis of needle56. Beam shaping electrodes 58 and 60 and the biasing voltages appliedthereto may improve the corona charging capability of the gun in twoimportant ways. First, lower electrode 60 may act as a mask for definingthe diameter of the area of corona deposition. Second, the bias voltageon electrode 60 (same polarity as the corona ions) repels ions thatnormally would be captured by the edge of electrode 60 and directs themdown to the specimen site with an enhanced density that abruptly ceasesunder the edge of electrode 60.

Upper electrode 58 may help to boost the efficiency of the corona sourceby being biased at a relatively high voltage (up to ±3 kV) with the samepolarity as the corona ions. Potentials in the range of ±6-9 kV and upto ±1.5 kV are appropriate for needle 56 and mask electrode 60,respectively. This may result in an electrical field configuration, inthe upper region of the corona source, that prevents many of the ionsfrom being captured by the upper electrode and directs them down tolower electrode 60 which, in turn, directs them to the specimen site. Itshould be noted that needle 56 and electrodes 58 and 60 may be supportedand insulated from each other by suitable insulated support members (notshown) that may allow for the application of the necessary biases.

FIG. 9 is essentially the same as FIG. 8 except for the importantdifference that two facing and horizontal needles 62 and 64 are providedin FIG. 9 in lieu of the single vertical needle 56 of FIG. 8. Thepotential applied to needles 62 and 64 and electrodes 58 and 60 of FIG.9 may be the same as the corresponding parts in the case of FIG. 8.

Additional examples of non-contact corona sources are illustrated inU.S. Pat. Nos. 4,599,558 to Castellano et al., 5,594,247 to Verkuil etal., and 5,644,223 to Verkuil and are incorporated by reference as iffully set forth herein. In an embodiment, a system as described herein,may include a non-contact work function sensor such as a Monroe probe inplace of a Kelvin probe. Further examples of work function sensors thatmay be incorporated into the system are illustrated in U.S. Pat. Nos.4,812,756 to Curtis et al., 5,650,731 to Fung, and 5,767,693 to Verkuil,which are incorporated by reference as if fully set forth herein. Inaddition, any other appropriate system and corona source known in theart may be used for carrying out a method as described herein.

The measurement system may be configured as described above. Anadditional example of an appropriate measurement system is the Quantoxor Quantox XP system, which is commercially available from KLA-Tencor.Further examples of appropriate measurement systems are illustrated inone or more of U.S. Pat. Nos. 5,594,247 to Verkuil et al., 5,767,693 toVerkuil, 5,834,941 to Verkuil, 6,060,709 to Verkuil et al., 6,072,320 toVerkuil, 6,091,257 to Verkuil et al., 6,097,196 to Verkuil et al.,6,104,206 to Verkuil, 6,121,783 to Horner et al., 6,191,605 to Miller etal., and 6,202,029 to Verkuil et al., which are incorporated byreference as if fully set forth herein. The measurement system may beconfigured as illustrated in any of these U.S. patents. Programinstructions implementing methods such as those described above may betransmitted over or stored on a carrier medium. The carrier medium maybe a transmission medium such as a wire, cable, or wireless transmissionlink, or a signal traveling along such a wire, cable, or link. Thecarrier medium may also be a storage medium such as a read-only memory,a random access memory, a magnetic or optical disk, or a magnetic tape.

In an embodiment, the computer system may be configured to execute theprogram instructions to perform a computer-implemented method accordingto the above embodiments. The computer system may take various forms,including a personal computer system, mainframe computer system,workstation, network appliance, Internet appliance, personal digitalassistant (“PDA”), television system or other device. In general, theterm “computer system” may be broadly defined to encompass any devicehaving a processor, which executes instructions from a memory medium.

The program instructions may be implemented in any of various ways,including procedure-based techniques, component-based techniques, and/orobject-oriented techniques, among others. For example, the programinstructions may be implemented using ActiveX controls, C++ objects,JavaBeans, Microsoft Foundation Classes (“MFC”), or other technologiesor methodologies, as desired.

It will be appreciated to those skilled in the art having the benefit ofthis disclosure that this invention is believed to provide methods andsystems for measurements of insulating film electrical thickness and/orcapacitance. Further modifications and alternative embodiments ofvarious aspects of the invention will be apparent to those skilled inthe art in view of this description. Accordingly, this description is tobe construed as illustrative only and is for the purpose of teachingthose skilled in the art the general manner of carrying out theinvention. It is to be understood that the forms of the invention shownand described herein are to be taken as the presently preferredembodiments. Elements and materials may be substituted for thoseillustrated and described herein, parts and processes may be reversed,and certain features of the invention may be utilized independently, allas would be apparent to one skilled in the art after having the benefitof this description of the invention. Changes may be made in theelements described herein without departing from the spirit and scope ofthe invention as described in the following claims.

What is claimed is:
 1. A method, comprising measuring a surfacepotential of a leaky insulating film without inducing leakage across theinsulating film and determining an electrical parameter of theinsulating film from the surface potential, wherein said determiningcomprises determining a potential of a substrate on which the insulatingfilm is formed, determining a pure voltage across the insulating filmfrom the surface potential and the substrate potential, and determiningthe electrical parameter of the insulating film from the pure voltage.2. The method of claim 1, wherein the electrical parameter comprisescapacitance or electrical thickness.
 3. The method of claim 1, furthercomprising applying an electrical field across the insulating film priorto said measuring, wherein leakage across the insulating film caused bythe electrical field is negligible.
 4. The method of claim 1, whereinthe electrical parameter comprises capacitance, the method furthercomprising obtaining an optical thickness from a host computer,determining a dielectric constant of the insulating film from thecapacitance and the optical thickness, and reporting the dielectricconstant to the host computer.
 5. The method of claim 1, wherein theelectrical parameter comprises capacitance, the method furthercomprising determining an optical or physical thickness of theinsulating film and determining a dielectric constant of the insulatingfilm from the capacitance and the optical or physical thickness.
 6. Themethod of claim 5, further comprising altering a parameter of a processtool in response to the dielectric constant using a feedback controltechnique, a feedforward control technique, or an in situ controltechnique.
 7. The method of claim 1, further comprising applying anelectrical field across the insulating film prior to said measuring,wherein the electrical field is about 0.0001 MV/cm to about 1 MV/cm. 8.The method of claim 1, further comprising applying an electrical fieldacross the insulating film prior to said measuring, wherein theelectrical field does not alter the electrical parameter of theinsulating film.
 9. The method of claim 1, wherein said determiningfurther comprises experimentally determining the potential of thesubstrate.
 10. The method of claim 1, wherein said determining furthercomprises theoretically determining the potential of the substrate. 11.The method of claim 1, wherein said measuring is performed withoutcontacting a surface of the insulating film.
 12. The method of claim 1,wherein said measuring comprises contacting a surface of the insulatingfilm.
 13. The method of claim 1, wherein said measuring is performed inthe presence of a background light.
 14. The method of claim 1, furthercomprising altering a parameter of a process tool in response to theelectrical parameter using a feedback control technique or a feedforwardcontrol technique.
 15. The method of claim 1, wherein the method isperformed during a semiconductor fabrication process.
 16. The method ofclaim 1, further comprising altering a parameter of a process tool inresponse to the electrical parameter using an in situ control technique.17. A method for determining an electrical parameter of an insulatingfilm, wherein a specimen comprises the insulating film formed on asubstrate, the method comprising: applying an electrical field acrossthe insulating film, wherein leakage across the insulating film causedby the electrical field is negligible, and wherein the insulating filmhas a thickness such that a potential of the substrate is negligible;measuring a surface voltage of the specimen; and determining theelectrical parameter of the insulating film from the surface voltage,wherein said determining comprises determining a pure voltage across theinsulating film from the surface voltage, and determining the electricalparameter of the insulating film from the pure voltage.
 18. The methodof claim 17, wherein the thickness is greater than about 400 Å.
 19. Themethod of claim 17, wherein said measuring comprises measuring thesurface voltage in accumulation, depletion, inversion, or a combinationthereof.